FreezeFrame

I have a dataframe with groups.
To normalize the values for each group I'd like to divide all values of each group by the value of a certain element within that group.
df = pd.DataFrame([['a','2018-02-03',42],
['a','2018-02-04',22],
['a','2018-02-05',10],
['a','2018-02-06',32],
['b','2018-02-03',10...